The point is more that 50 years ago, people thought we had sufficient understanding of fusion to build something like this. And thanks to advancements in inerti

The point is more that 50 years ago, people thought we had sufficient understanding of fusion to build something like this. And thanks to advancements in inertial confinement research at the height of the thermonuclear arms race, they actually had a pretty good reason to believe so back then. There is very little reason to believe these new companies today when they say so, because fusion research is in a deep hole and running on a fraction of the funding it did during the cold war.